13
GCUF/GRUF Vent-Free Fireboxes
Monessen • GCUF/GRUF Owner Manual • 71D0530 • Rev G • 01/20
COMBUSTION AIR
WARNING!
DO NOT remove the cover if the outside air
will not be connected.
The use of outside air for combustion is optional unless
required by building codes. It is only necessary to supply
outside combustion air to one side of the fireplace. Use the
model AK4 combustion air kit.
MODEL AK4 COMBUSTION AIR ASSEMBLY
1. Remove the cover plate from the 4" outlet opening
location on the left or right outside of the fireplace.
2. Place the insulation ring between the AK4 starting collar
and fireplace wall.
3. Place the starting collar (4") into the hole on the side
of fireplace. Fasten it in place with the four sheet metal
screws provided.
Figures 16 and 17
NOTE: The air starting collar extends through the
fireplace outer wrap. When the air starting collar
is securely attached, it will form a seal against the
fireplace wall.
FP1900
OA start collar
8/08
Figure 16 -
Attach Outside Air Starting Collar and Insulation
Ring to Left Side of Fireplace
Insulation
Ring
AK4 Starting
Collar
Sheet Meal
Screws
Left Side of
Fireplace
Shorter End
of Air Starting
Collar
4. Attach outside duct to starting collar with duct clamp or
screws.
Figure 17
5. Cut a 6-inch diameter opening for model AK4 in the
outside wall covering where the outside vent is to be
located.
Figure 18
6. Select and cut a piece of duct long enough to attach to
the fireplace and stick out at least 3" beyond the face of
the wall to which the AK4 inlet air vent will be attached.
Cut duct with a standard pocket knife.
Figure 17
FP2700
OA duct
Screws
Air Starting
Collar
Duct
Left Side of
Fireplace
FP2700
Figure 17 -
Attach Outside Duct to Starting Collar
FP1904
AK4 install
8/08
6"
Diameter
Hole
Duct
Extending
3" Min.
Screws
Nail
Hole
Screws
AK4 Inlet Air
Vent
Figure 18 -
Combustion Air Assembly for Model
AK4
FP1904
WARNING!
Use FP-4 U duct for maximum efficiency and
safety. Do not use a combustible duct. Always
use UL Listed Class 0 or 1 duct material.
